Threads and processes

Processes are the smallest unit of resource allocation and threads are the smallest unit of CPU scheduling

  • A thread moves under a process
  • A process can contain multiple threads
  • Data is difficult to share between different processes
  • Data is easily shared between threads in the same process

How threads are created

Inheriting the Thread class

1. Define a class that inherits the Thread class and overrides the run method

public class MyThread extends Thread {
    @Override
    public void run(a) {
        System.out.println("I inherit Thread."); }}Copy the code

2. Start a new Thread by calling the start method in the Thread class

Note: What is the difference between calling the run method directly and the start method?

  • You can call the run method directly, but you don’t start a separate thread;
  • Calling the start method opens a separate new thread and calls the run method;
public static void main(String[] args) {
    System.out.println("111111");
    MyThread t1 = new MyThread();
    t1.start();
    System.out.println("22222");
}
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The result is that the run method of thread T1, which prints the statement before executing the main statement, is two different threads

Implement the Runnable interface mode

1. Define a custom class that implements the Runnable interface and overwrites the Run method

public class MyThread2 implements Runnable{
    @Override
    public void run(a) {
        System.out.println("I'm a class that implements the Runnable interface..."); }}Copy the code

2. Invoke the Thread(Runnable target) method to create a Thread object

public static void main(String[] args) {
    System.out.println("111111");
    Thread t2 = new Thread(new MyThread2());
    t2.start();
    System.out.println("22222");
}
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Results:

If the thread is used once, you can also use anonymous inner classes

public static void main(String[] args) {
    System.out.println("111111");
    Thread t3 = new Thread(new Runnable() {
        @Override
        public void run(a) {
            System.out.println("I'm anonymous inner class."); }}); t3.start(); System.out.println("22222");
}
Copy the code

Result: Same effect